1. FIELD OF THE INVENTION
The present invention relates to adjustable roof support mechanisms for supporting roofs of mines, and more particularly to the roof cap assemblies used in such roof support mechanisms.
2. THE PRIOR ART
Adjustable roof support mechanisms for supporting the roofs of mines are well known. Such roof support mechanisms can include a roof cap assembly, which includes a main cap, a forward cap that is pivotally connected to the forward end of the main cap in a cantilever fashion, the forward cap having a front tip for contacting the roof of the mine, and supporting cylinders that are connected between the main cap and the forward cap to control the orientation of the forward cap relative to the main cap; a breakage shield which is connected to the rear end of the main cap of the roof cap assembly; one or more foot elements which rest on the floor of the mine; a plurality of connecting arms which connect the rear end of the foot element(s) to the rear end of the breakage shield, and one or more extendable strut (prop) elements which extend upwardly from the foot element(s) to the main cap of the roof cap assembly. See, for example, U.S. Pat. No. 4,293,246, British Patent No. 1,249,412 and German Patent No. 36 13 765.
Known roof cap assemblies of such roof support mechanisms utilize supporting cylinders that include two pressure medium connections, one for supplying pressure medium to the cylinder chamber between the head of the piston and the end wall of the cylinder and the other for supplying pressure medium to the annulus between the piston rod and the side wall of the cylinder. Since these known supporting cylinders are operated with pressure mediums under normal pressures, the roof supporting mechanisms in which they are used must utilize at least three of them between the main cap and the forward cap, i.e., in spaced apart relationship across their widths, so that the front tip of the forward cap can be set against the mine roof with the necessary force. However, the areas occupied by the supporting cylinders cannot be used by other components, such as control elements.
The object of the present invention is to provide a supporting cylinder of the aforementioned kind which is constructed such that a roof cap assembly using such supporting cylinders needs only two of them, at spaced locations across the widths of the main cap and the forward cap, yet can assure the necessary force applied by the front tip of the forward cap against the mine roof.